SPARK-1911: Emphasize that Spark jars should be built with Java 6.
SPARK-1911: Emphasize that Spark jars should be built with Java 6.

This commit requires the user to manually say "yes" when buiding Spark
without Java 6. The prompt can be bypassed with a flag (e.g. if the user
is scripting around make-distribution).

Author: Patrick Wendell <pwendell@gmail.com>

Closes #859 from pwendell/java6 and squashes the following commits:

4921133 [Patrick Wendell] Adding Pyspark Notice
fee8c9e [Patrick Wendell] SPARK-1911: Emphasize that Spark jars should be built with Java 6.

ddna1021/spark,techaddict/spark,ioana-delaney/spark,Aegeaner/spark,mahak/spark,ueshin/apache-spark,caneGuy/spark,skonto/spark,Aegeaner/spark,icexelloss/spark,saltstar/spark,JerryLead/spark,1haodian/spark,aray/spark,rekhajoshm/spark,apache-spark-on-k8s/spark,zero323/spark,zzcclp/spark,loneknightpy/spark,techaddict/spark,bravo-zhang/spark,goldmedal/spark,andrewor14/spark,esi-mineset/spark,alunarbeach/spark,stanzhai/spark,icexelloss/spark,dhruve/spark,esi-mineset/spark,jrshust/spark,jianran/spark,akopich/spark,janewangfb/spark,witgo/spark,aosagie/spark,kissmetrics/spark,srowen/spark,gioenn/xSpark,sureshthalamati/spark,nlalevee/spark,JoshRosen/spark,esi-mineset/spark,sureshthalamati/spark,nlalevee/spark,liutang123/spark,dongjoon-hyun/spark,vinodkc/spark,byakuinss/spark,brad-kaiser/spark,shubhamchopra/spark,cloud-fan/spark,ueshin/apache-spark,rekhajoshm/spark,sachintyagi22/spark,saturday-shi/spark,nchammas/spark,poffuomo/spark,adrian-ionescu/apache-spark,big-pegasus/spark,WeichenXu123/spark,someorz/spark,guoxiaolongzte/spark,ibm-research-ireland/sparkoscope,minixalpha/spark,facaiy/spark,JoshRosen/spark,ibm-research-ireland/sparkoscope,shubhamchopra/spark,alunarbeach/spark,jlopezmalla/spark,cloud-fan/spark,map222/spark,cloud-fan/spark,ptkool/spark,dhruve/spark,guoxiaolongzte/spark,WeichenXu123/spark,gioenn/xSpark,ibm-research-ireland/sparkoscope,UndeadBaneGitHub/spark,alunarbeach/spark,goldmedal/spark,vinodkc/spark,jianran/spark,gengliangwang/spark,jrshust/spark,kevinyu98/spark,caneGuy/spark,gioenn/xSpark,maropu/spark,someorz/spark,ddna1021/spark,big-pegasus/spark,kissmetrics/spark,ibm-research-ireland/sparkoscope,Panos-Bletsos/spark-cost-model-optimizer,eyalfa/spark,lxsmnv/spark,sachintyagi22/spark,saltstar/spark,hhbyyh/spark,minixalpha/spark,kiszk/spark,cin/spark,map222/spark,aosagie/spark,holdenk/spark,kiszk/spark,kissmetrics/spark,vinodkc/spark,huang1900/spark,kiszk/spark,huang1900/spark,shaneknapp/spark,chuckchen/spark,andrewor14/spark,caneGuy/spark,brad-kaiser/spark,aokolnychyi/spark,LantaoJin/spark,MLnick/spark,zzcclp/spark,skonto/spark,debugger87/spark,narahari92/spark,ueshin/apache-spark,byakuinss/spark,rikima/spark,xflin/spark,mzl9039/spark,joseph-torres/spark,panfengfeng/spark,ron8hu/spark,narahari92/spark,ajaysaini725/spark,gioenn/xSpark,alunarbeach/spark,xflin/spark,cloud-fan/spark,chuckchen/spark,rekhajoshm/spark,WindCanDie/spark,poffuomo/spark,darionyaphet/spark,adrian-ionescu/apache-spark,map222/spark,byakuinss/spark,aosagie/spark,MLnick/spark,highfei2011/spark,ibm-research-ireland/sparkoscope,szhem/spark,akopich/spark,dongjoon-hyun/spark,andrewor14/iolap,Aegeaner/spark,joseph-torres/spark,chuckchen/spark,shuangshuangwang/spark,taroplus/spark,witgo/spark,lvdongr/spark,xuanyuanking/spark,sureshthalamati/spark,eyalfa/spark,goldmedal/spark,haowu80s/spark,dhruve/spark,debugger87/spark,minixalpha/spark,rednaxelafx/apache-spark,wangyum/spark,markhamstra/spark,spark-test/spark,publicRoman/spark,loneknightpy/spark,publicRoman/spark,icexelloss/spark,kissmetrics/spark,guoxiaolongzte/spark,setjet/spark,sahilTakiar/spark,andrewor14/spark,mike0sv/spark,jiangxb1987/spark,liutang123/spark,holdenk/spark,ajaysaini725/spark,bravo-zhang/spark,darionyaphet/spark,pgandhi999/spark,debugger87/spark,kevinyu98/spark,mike0sv/spark,joseph-torres/spark,gioenn/xSpark,maropu/spark,highfei2011/spark,maropu/spark,ConeyLiu/spark,lvdongr/spark,zhouyejoe/spark,wzhfy/spark,facaiy/spark,mike0sv/spark,WeichenXu123/spark,lxsmnv/spark,someorz/spark,akopich/spark,jiangxb1987/spark,JerryLead/spark,jiangxb1987/spark,skonto/spark,liutang123/spark,publicRoman/spark,liutang123/spark,publicRoman/spark,hvanhovell/spark,aokolnychyi/spark,maropu/spark,cin/spark,skonto/spark,hhbyyh/spark,shuangshuangwang/spark,rekhajoshm/spark,ConeyLiu/spark,xuanyuanking/spark,icexelloss/spark,mdespriee/spark,nchammas/spark,wangmiao1981/spark,loneknightpy/spark,jrshust/spark,zuotingbing/spark,ron8hu/spark,setjet/spark,skonto/spark,milliman/spark,WeichenXu123/spark,wzhfy/spark,icexelloss/spark,szhem/spark,saltstar/spark,nlalevee/spark,hhbyyh/spark,WindCanDie/spark,ron8hu/spark,nilsgrabbert/spark,zhouyejoe/spark,adrian-ionescu/apache-spark,esi-mineset/spark,Aegeaner/spark,liyichao/spark,bdrillard/spark,gengliangwang/spark,map222/spark,kimoonkim/spark,aray/spark,ioana-delaney/spark,someorz/spark,liutang123/spark,debugger87/spark,bdrillard/spark,hhbyyh/spark,andrewor14/iolap,tejasapatil/spark,markhamstra/spark,bdrillard/spark,aray/spark,rednaxelafx/apache-spark,cloud-fan/spark,bOOm-X/spark,mahak/spark,wangmiao1981/spark,narahari92/spark,zuotingbing/spark,shaneknapp/spark,adrian-ionescu/apache-spark,someorz/spark,pronix/spark,Panos-Bletsos/spark-cost-model-optimizer,ibm-research-ireland/sparkoscope,ptkool/spark,kimoonkim/spark,andrewor14/iolap,setjet/spark,spark-test/spark,sachintyagi22/spark,kevinyu98/spark,jianran/spark,saturday-shi/spark,byakuinss/spark,zhouyejoe/spark,hhbyyh/spark,apache/spark,janewangfb/spark,spark-test/spark,LantaoJin/spark,mdespriee/spark,SnappyDataInc/spark,WeichenXu123/spark,rekhajoshm/spark,huang1900/spark,darionyaphet/spark,map222/spark,setjet/spark,zhouyejoe/spark,liyichao/spark,Panos-Bletsos/spark-cost-model-optimizer,vinodkc/spark,aosagie/spark,nlalevee/spark,haowu80s/spark,michalsenkyr/spark,saturday-shi/spark,zero323/spark,bOOm-X/spark,Aegeaner/spark,BryanCutler/spark,mike0sv/spark,jrshust/spark,gengliangwang/spark,facaiy/spark,1haodian/spark,LantaoJin/spark,dhruve/spark,WindCanDie/spark,liyichao/spark,caneGuy/spark,BryanCutler/spark,apache-spark-on-k8s/spark,haowu80s/spark,kiszk/spark,mzl9039/spark,apache-spark-on-k8s/spark,aokolnychyi/spark,metamx/spark,SnappyDataInc/spark,narahari92/spark,mahak/spark,ConeyLiu/spark,WindCanDie/spark,apache/spark,bravo-zhang/spark,apache-spark-on-k8s/spark,andrewor14/spark,poffuomo/spark,rezasafi/spark,tengpeng/spark,markhamstra/spark,michalsenkyr/spark,szhem/spark,metamx/spark,saturday-shi/spark,liyichao/spark,eyalfa/spark,markhamstra/spark,WindCanDie/spark,kevinyu98/spark,SHASHANKB/spark,rednaxelafx/apache-spark,zzcclp/spark,BryanCutler/spark,esi-mineset/spark,stanzhai/spark,shuangshuangwang/spark,UndeadBaneGitHub/spark,patrick-nicholson/spark,pronix/spark,nchammas/spark,goldmedal/spark,wzhfy/spark,cin/spark,ueshin/apache-spark,cin/spark,metamx/spark,shaneknapp/spark,brad-kaiser/spark,hhbyyh/spark,WeichenXu123/spark,gioenn/xSpark,Aegeaner/spark,mdespriee/spark,apache-spark-on-k8s/spark,shaneknapp/spark,SnappyDataInc/spark,aray/spark,ddna1021/spark,SHASHANKB/spark,1haodian/spark,nchammas/spark,BryanCutler/spark,techaddict/spark,rezasafi/spark,tejasapatil/spark,alunarbeach/spark,jrshust/spark,pgandhi999/spark,adrian-ionescu/apache-spark,spark-test/spark,yanboliang/spark,shuangshuangwang/spark,aosagie/spark,jkbradley/spark,mzl9039/spark,andrewor14/iolap,bravo-zhang/spark,sureshthalamati/spark,panfengfeng/spark,dbtsai/spark,bdrillard/spark,huang1900/spark,highfei2011/spark,ahnqirage/spark,MLnick/spark,taroplus/spark,liutang123/spark,mike0sv/spark,Panos-Bletsos/spark-cost-model-optimizer,wangyum/spark,lxsmnv/spark,zhouyejoe/spark,ddna1021/spark,big-pegasus/spark,xuanyuanking/spark,kiszk/spark,lxsmnv/spark,holdenk/spark,kimoonkim/spark,hvanhovell/spark,tejasapatil/spark,shubhamchopra/spark,stanzhai/spark,shubhamchopra/spark,highfei2011/spark,nilsgrabbert/spark,tengpeng/spark,sachintyagi22/spark,markhamstra/spark,ericvandenbergfb/spark,gengliangwang/spark,aokolnychyi/spark,ConeyLiu/spark,HyukjinKwon/spark,patrick-nicholson/spark,icexelloss/spark,nchammas/spark,matthewfranglen/spark,HyukjinKwon/spark,ahnqirage/spark,bOOm-X/spark,nilsgrabbert/spark,mdespriee/spark,guoxiaolongzte/spark,janewangfb/spark,skonto/spark,lvdongr/spark,actuaryzhang/spark,saltstar/spark,wangmiao1981/spark,milliman/spark,zhouyejoe/spark,facaiy/spark,taroplus/spark,tengpeng/spark,rikima/spark,kissmetrics/spark,alunarbeach/spark,dongjoon-hyun/spark,guoxiaolongzte/spark,rezasafi/spark,chuckchen/spark,byakuinss/spark,shubhamchopra/spark,esi-mineset/spark,rikima/spark,haowu80s/spark,akopich/spark,apache-spark-on-k8s/spark,andrewor14/spark,holdenk/spark,holdenk/spark,zzcclp/spark,apache/spark,HyukjinKwon/spark,darionyaphet/spark,metamx/spark,sachintyagi22/spark,aokolnychyi/spark,apache-spark-on-k8s/spark,ajaysaini725/spark,rednaxelafx/apache-spark,srowen/spark,pgandhi999/spark,eyalfa/spark,liutang123/spark,Aegeaner/spark,xflin/spark,adrian-ionescu/apache-spark,JoshRosen/spark,metamx/spark,rednaxelafx/apache-spark,dhruve/spark,yanboliang/spark,tejasapatil/spark,eyalfa/spark,apache/spark,techaddict/spark,dhruve/spark,wangyum/spark,ioana-delaney/spark,andrewor14/spark,techaddict/spark,jlopezmalla/spark,joseph-torres/spark,pronix/spark,liyichao/spark,dbtsai/spark,sahilTakiar/spark,dbtsai/spark,byakuinss/spark,ConeyLiu/spark,witgo/spark,JerryLead/spark,mike0sv/spark,sahilTakiar/spark,vinodkc/spark,minixalpha/spark,zuotingbing/spark,zuotingbing/spark,witgo/spark,setjet/spark,rikima/spark,publicRoman/spark,goldmedal/spark,dbtsai/spark,kimoonkim/spark,pronix/spark,milliman/spark,michalsenkyr/spark,jkbradley/spark,kevinyu98/spark,caneGuy/spark,ericvandenbergfb/spark,michalsenkyr/spark,SHASHANKB/spark,jlopezmalla/spark,cin/spark,JerryLead/spark,JerryLead/spark,hvanhovell/spark,minixalpha/spark,zero323/spark,ericvandenbergfb/spark,HyukjinKwon/spark,cin/spark,hvanhovell/spark,janewangfb/spark,yanboliang/spark,eyalfa/spark,nilsgrabbert/spark,andrewor14/iolap,mahak/spark,WeichenXu123/spark,haowu80s/spark,rikima/spark,ptkool/spark,wangmiao1981/spark,jlopezmalla/spark,gengliangwang/spark,SHASHANKB/spark,xflin/spark,janewangfb/spark,stanzhai/spark,dbtsai/spark,ron8hu/spark,hvanhovell/spark,facaiy/spark,dbtsai/spark,jianran/spark,ahnqirage/spark,guoxiaolongzte/spark,goldmedal/spark,jlopezmalla/spark,chuckchen/spark,panfengfeng/spark,ahnqirage/spark,actuaryzhang/spark,aray/spark,witgo/spark,akopich/spark,taroplus/spark,jianran/spark,loneknightpy/spark,ddna1021/spark,joseph-torres/spark,tengpeng/spark,rezasafi/spark,chuckchen/spark,witgo/spark,jiangxb1987/spark,zhouyejoe/spark,shuangshuangwang/spark,kimoonkim/spark,nchammas/spark,mdespriee/spark,ptkool/spark,ahnqirage/spark,aokolnychyi/spark,tengpeng/spark,xflin/spark,1haodian/spark,SnappyDataInc/spark,ericvandenbergfb/spark,ahnqirage/spark,huang1900/spark,apache/spark,MLnick/spark,markhamstra/spark,UndeadBaneGitHub/spark,mdespriee/spark,dongjoon-hyun/spark,ueshin/apache-spark,szhem/spark,brad-kaiser/spark,SnappyDataInc/spark,bravo-zhang/spark,map222/spark,SnappyDataInc/spark,jlopezmalla/spark,patrick-nicholson/spark,taroplus/spark,Panos-Bletsos/spark-cost-model-optimizer,pgandhi999/spark,jrshust/spark,xuanyuanking/spark,jkbradley/spark,actuaryzhang/spark,kevinyu98/spark,ajaysaini725/spark,sahilTakiar/spark,huang1900/spark,gengliangwang/spark,dongjoon-hyun/spark,cloud-fan/spark,saltstar/spark,big-pegasus/spark,sachintyagi22/spark,yanboliang/spark,minixalpha/spark,xuanyuanking/spark,jkbradley/spark,nilsgrabbert/spark,poffuomo/spark,techaddict/spark,jrshust/spark,pgandhi999/spark,lvdongr/spark,srowen/spark,ioana-delaney/spark,actuaryzhang/spark,ConeyLiu/spark,holdenk/spark,aray/spark,akopich/spark,kimoonkim/spark,HyukjinKwon/spark,zero323/spark,wangyum/spark,panfengfeng/spark,hhbyyh/spark,tejasapatil/spark,bOOm-X/spark,debugger87/spark,narahari92/spark,JerryLead/spark,apache/spark,dhruve/spark,xflin/spark,BryanCutler/spark,nilsgrabbert/spark,nlalevee/spark,yanboliang/spark,spark-test/spark,darionyaphet/spark,bdrillard/spark,LantaoJin/spark,brad-kaiser/spark,rikima/spark,zero323/spark,chuckchen/spark,icexelloss/spark,zero323/spark,UndeadBaneGitHub/spark,aray/spark,facaiy/spark,mzl9039/spark,ddna1021/spark,LantaoJin/spark,panfengfeng/spark,rezasafi/spark,lxsmnv/spark,mahak/spark,bravo-zhang/spark,panfengfeng/spark,rednaxelafx/apache-spark,nlalevee/spark,tengpeng/spark,UndeadBaneGitHub/spark,ueshin/apache-spark,wangyum/spark,mahak/spark,bOOm-X/spark,kiszk/spark,andrewor14/iolap,eyalfa/spark,sureshthalamati/spark,andrewor14/iolap,aosagie/spark,JoshRosen/spark,markhamstra/spark,jianran/spark,bOOm-X/spark,minixalpha/spark,stanzhai/spark,wangmiao1981/spark,srowen/spark,JoshRosen/spark,publicRoman/spark,metamx/spark,pronix/spark,szhem/spark,narahari92/spark,sureshthalamati/spark,big-pegasus/spark,ahnqirage/spark,wangmiao1981/spark,saturday-shi/spark,bOOm-X/spark,darionyaphet/spark,1haodian/spark,yanboliang/spark,SHASHANKB/spark,spark-test/spark,maropu/spark,JoshRosen/spark,spark-test/spark,shuangshuangwang/spark,actuaryzhang/spark,jiangxb1987/spark,mdespriee/spark,sahilTakiar/spark,LantaoJin/spark,aokolnychyi/spark,pronix/spark,tejasapatil/spark,loneknightpy/spark,tengpeng/spark,facaiy/spark,publicRoman/spark,shubhamchopra/spark,nchammas/spark,ConeyLiu/spark,lvdongr/spark,someorz/spark,lvdongr/spark,big-pegasus/spark,rekhajoshm/spark,milliman/spark,ioana-delaney/spark,ericvandenbergfb/spark,UndeadBaneGitHub/spark,wzhfy/spark,zzcclp/spark,saturday-shi/spark,milliman/spark,milliman/spark,patrick-nicholson/spark,kiszk/spark,brad-kaiser/spark,sureshthalamati/spark,lxsmnv/spark,xuanyuanking/spark,ron8hu/spark,cin/spark,szhem/spark,huang1900/spark,tejasapatil/spark,LantaoJin/spark,map222/spark,bravo-zhang/spark,jlopezmalla/spark,rezasafi/spark,ericvandenbergfb/spark,saltstar/spark,holdenk/spark,janewangfb/spark,patrick-nicholson/spark,brad-kaiser/spark,WindCanDie/spark,byakuinss/spark,metamx/spark,ajaysaini725/spark,saltstar/spark,wzhfy/spark,pgandhi999/spark,taroplus/spark,cloud-fan/spark,loneknightpy/spark,zuotingbing/spark,hvanhovell/spark,alunarbeach/spark,goldmedal/spark,yanboliang/spark,gioenn/xSpark,pgandhi999/spark,ueshin/apache-spark,Panos-Bletsos/spark-cost-model-optimizer,bdrillard/spark,BryanCutler/spark,JerryLead/spark,skonto/spark,michalsenkyr/spark,MLnick/spark,JoshRosen/spark,nilsgrabbert/spark,caneGuy/spark,Panos-Bletsos/spark-cost-model-optimizer,wangyum/spark,ajaysaini725/spark,sahilTakiar/spark,taroplus/spark,mzl9039/spark,xuanyuanking/spark,ddna1021/spark,1haodian/spark,stanzhai/spark,ajaysaini725/spark,ioana-delaney/spark,bdrillard/spark,ron8hu/spark,setjet/spark,saturday-shi/spark,michalsenkyr/spark,ptkool/spark,narahari92/spark,caneGuy/spark,xflin/spark,liyichao/spark,patrick-nicholson/spark,loneknightpy/spark,big-pegasus/spark,MLnick/spark,janewangfb/spark,highfei2011/spark,kissmetrics/spark,maropu/spark,sahilTakiar/spark,zuotingbing/spark,HyukjinKwon/spark,SHASHANKB/spark,kevinyu98/spark,zuotingbing/spark,akopich/spark,ibm-research-ireland/sparkoscope,mike0sv/spark,wangyum/spark,1haodian/spark,hvanhovell/spark,sachintyagi22/spark,zzcclp/spark,highfei2011/spark,shaneknapp/spark,kimoonkim/spark,darionyaphet/spark,aosagie/spark,dongjoon-hyun/spark,apache/spark,mzl9039/spark,setjet/spark,gengliangwang/spark,UndeadBaneGitHub/spark,shuangshuangwang/spark,srowen/spark,poffuomo/spark,witgo/spark,SnappyDataInc/spark,dbtsai/spark,milliman/spark,ioana-delaney/spark,rezasafi/spark,poffuomo/spark,techaddict/spark,rikima/spark,shubhamchopra/spark,ron8hu/spark,adrian-ionescu/apache-spark,zero323/spark,liyichao/spark,shaneknapp/spark,patrick-nicholson/spark,maropu/spark,jkbradley/spark,wangmiao1981/spark,SHASHANKB/spark,shaneknapp/spark,vinodkc/spark,actuaryzhang/spark,vinodkc/spark,mahak/spark,michalsenkyr/spark,debugger87/spark,rekhajoshm/spark,jianran/spark,BryanCutler/spark,srowen/spark,MLnick/spark,HyukjinKwon/spark,szhem/spark,joseph-torres/spark,jkbradley/spark,lvdongr/spark,jiangxb1987/spark,debugger87/spark,srowen/spark,wzhfy/spark,jiangxb1987/spark,WindCanDie/spark,ericvandenbergfb/spark,someorz/spark,andrewor14/spark,guoxiaolongzte/spark,haowu80s/spark,ptkool/spark,ptkool/spark,lxsmnv/spark,nlalevee/spark,jkbradley/spark,dongjoon-hyun/spark,poffuomo/spark,wzhfy/spark,rednaxelafx/apache-spark,panfengfeng/spark,esi-mineset/spark,zzcclp/spark,joseph-torres/spark,mzl9039/spark,actuaryzhang/spark,stanzhai/spark,highfei2011/spark,kissmetrics/spark